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Posted by: Root_Werks Dec 23 2022, 12:19 PM

Running my 2.7 CIS can sometimes starve for fuel (or not enough PSIG). I know it's because the supply line from the tank to the 911 CIS fuel pump is the tiny stock size (5mm?). The supply to the pump looks twice the size although I think it's only 8mm. I have a simply brass adapter that sort of sucks. It's a brass 5/16 to 3/8 which doesn't seem like an elegant solution.

Generic pic of a fuel tank for reference:




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Posted by: Root_Werks Dec 23 2022, 12:23 PM

I did buy a couple of tank supply fittings from VW speed shops hoping they'd be a little larger. Oddly, the screens and washers matched up to the stock 914 fittings perfectly. Tubes were same size.

If I run full lead-foot through 1st-2nd, fuel can keep up because it's only at peak RPM for a few seconds. Anything 3rd and up and the fuel pump can't keep up, rather the supply to the fuel (gravity and little fitting) can't supply enough to keep the PSIG needed to operate the CIS correctly.

Anybody have any luck with any larger supply fitting?




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Posted by: Root_Werks Dec 23 2022, 12:24 PM

Bad pic in previous post, the two kits I bought both had metal mesh screens like this one:




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Posted by: mb911 Dec 23 2022, 12:55 PM

To be honest I am not sure I buy that. Plenty of folks using hot 3.6 engines with the stock fittings.

Posted by: bdstone914 Dec 23 2022, 01:01 PM

You can tap the inside of the threaded nipples for 1/4 Male pipe thread and install the fitting type of your choice. I like a -6 AN that can be easily removed. You need an external fiel filter.

Posted by: Root_Werks Dec 23 2022, 01:03 PM

Interesting, I'll check my rubber lines again. It happened once before a kink started to develop on the rubber line from tank to pump. Could be a partial kink?

Isn't the 911 tank supply line fitting from strainer 10mm? You'd think there'd be a reason it'd be size matched to the CIS pump.



If I'm incorrect, I'll apologize for asking the question and wasting forum thread space.

Posted by: Superhawk996 Dec 23 2022, 01:15 PM

With Ben

1/4” is 1mm bigger than 5mm

1/4” tube will flow about 30 gallons per hour at 30’ length

A 914 is much shorter than 30’ (both ways) and there is no way a 2.7l is consuming 30 GPH of fuel at normal road speeds.

I don’t have parts in front of me to measure but thought supply line was more like 8mm and the return was the smaller (5mm) line?

Partially plugged sock strainer in the tank as other potential issue? Dirty - constricted fuel filter? Pump and/or regulator going south? Improperly rated fuel hose on the suction side of the pump collapsing? Fuel tank vented properly? CIS fuel distributor in need of rebuild? Sticking or binding of CIS air sensor plate / balance beam?

Lots of other more plausible suspects for starvation at high RPM.

Posted by: mb911 Dec 23 2022, 02:04 PM

My guess is blocked or kinked line somewhere.

Posted by: Olympic 914 Dec 23 2022, 02:24 PM

Had a kinked line on mine once, feed line for the pump. would idle fine but under load the line would suck shut and stall the car. would start right back up every time.

Put a camera on the pressure gauge and could watch it drop.

Link to video post #8

http://www.914world.com/bbs2/index.php?showtopic=352435&hl=